KVM: selftests: Explicitly close guest_memfd files in some gmem tests

Explicitly close() guest_memfd files in various guest_memfd and
private_mem_conversions tests, there's no reason to keep the files open
until the test exits.

Fixes: 8a89efd4 ("KVM: selftests: Add basic selftest for guest_memfd()")
Fixes: 43f623f3 ("KVM: selftests: Add x86-only selftest for private memory conversions")
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Link: https://lore.kernel.org/r/20240227015716.27284-1-dongli.zhang@oracle.com
[sean: massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>

tools/testing/selftests/kvm/guest_memfd_test.c

@@ -167,6 +167,9 @@ static void test_create_guest_memfd_multiple(struct kvm_vm *vm)
 	TEST_ASSERT(ret != -1, "memfd fstat should succeed");
 	TEST_ASSERT(st1.st_size == 4096, "first memfd st_size should still match requested size");
 	TEST_ASSERT(st1.st_ino != st2.st_ino, "different memfd should have different inode numbers");
+
+	close(fd2);
+	close(fd1);
 }
 
 int main(int argc, char *argv[])

tools/testing/selftests/kvm/x86_64/private_mem_conversions_test.c

@@ -434,6 +434,8 @@ static void test_mem_conversions(enum vm_mem_backing_src_type src_type, uint32_t
 
 	r = fallocate(memfd, FALLOC_FL_KEEP_SIZE, 0, memfd_size);
 	TEST_ASSERT(!r, __KVM_SYSCALL_ERROR("fallocate()", r));
+
+	close(memfd);
 }
 
 static void usage(const char *cmd)